Conventionally, the surface of a resin molded component has been painted or plated so as to be provided with a surface so as to provide a metallic appearance and a bright appearance. Such a molded component may also be used as a design element in a vehicle, and a typical example thereof is an interior door handle provided in the cabin interior of a vehicle door. In recent years, however, the use of volatile organic compounds used in painting, etc., is required to be decreased because these compounds are environmental pollutants. Therefore, for example, a molded component having a metallic appearance may be manufactured by using a material to which a brightening agent such as aluminum powder or mica powder is added.
It is generally thought that a submarine gate type injection molding die may be used as a die for manufacturing the above-described molded component because the gate cut can be performed automatically. The injection molding die includes a gate for injecting material and a product portion for molding, and the gate and the product portion are connected to each other. Therefore, the manufactured molded component includes a gate portion formed by a resin material filled into the gate and a body portion formed by a resin material filled into the product portion, and the gate portion and the body portion are formed integrally. After injection molding, the gate portion becomes unnecessary, and so the gate portion must be cut from the body portion. To cut the gate portion from the body portion, a so-called gate cut for cutting the gate portion is performed. For the submarine gate type injection molding die, the gate cut is performed automatically by using the force of an ejector pin provided to remove the molded component from the die.
The gate portion is formed so as to have a cross-sectional area that is as small as about 0.0007-1.1301 mm2, so that the gate portion can be cut easily. However, this small cross-sectional area restricts the quantity of filling resin material into the product portion, so that a problems such as a short shot or a sink mark may be liable to occur. Furthermore, there arises a problem in that this die cannot be applied to a large component requiring a large filling amount of material. Also, another problem arises in that since a shearing force is applied to around the gate portion of the molded component itself at the time of cutting of the gate portion, jetting, silver streaking, and the like occur around the gate portion of the molded component, which may result in inferior appearance. In addition, there arises a problem in that the inferior appearance may be pronounced when a molding material to which a brightening agent is added is used.
Accordingly, to prevent the occurrence of jetting and silver streaking, it is thought that the gate cut may be performed manually with high accuracy, instead of being performed automatically. In this case, a side gate type injection molding die is mainly used. The side gate type injection molding die is formed so that the cross-sectional area of the gate portion is larger than that of the submarine gate type injection molding die. Therefore, the filling amount of material at the time of injection increases, so that a problem such as a short shot and a sink mark is less liable to occur, which offers an advantage that the die can be applied to a larger component.
On the other hand, the side gate type injection molding die has a problem of generating a weld line L. FIG. 7 shows, in enlargement, the outline of a gate remnant of a gate portion 102 provided on a body portion 101 of a general molded component 100. The feature is such that a resin material passes through the gate portion 102 and thereby the body portion 101 is injection molded. The gate portion 102 is connected to the body portion 101 by a contact part 104, and the contact part 104 has a substantially rectangular cross section. The weld line L originates from a corner part 104a of the cross section of the contact part 104 of the molded component 100 so as to extend radially.
Such a weld line L is generated in the case in which the resin materials flowing from different directions collide with each other in a part near the corner part 104a, and these resin materials do not mix with each other. In the case in which a conventional resin material, to which no brightening agent is added, is used, the colliding resin materials mix with each other, so that the weld line L is barely generated. However in the case in which the resin material to which a brightening agent is added is used, the brightening agent added to the colliding resin materials is oriented, and therefore the resin materials do not mix with each other, so that the weld line L is generated. The generation of such a weld line L presents a problem in that the appearance of the molded component 100 is degraded remarkably by the weld line L and the strength of the molded component 100 becomes insufficient in a part where the weld line L is generated.
To suppress the generation of the weld line, measures are taken regarding the material. In Japanese Unexamined Patent Application Publication No. 8-41284, the generation of the weld line is suppressed by selecting the shape and grain diameter of the brightening agent added to the resin material. Also, in Japanese Unexamined Patent Application Publication No. 8-239505, the generation of the weld line is suppressed by selecting the grain diameter and addition amount of brightening agent and by adding titanium oxide, lead oxide, zinc oxide, or antimony oxide, as a weld eliminating agent.
However, for the measures disclosed in Japanese Unexamined Patent Application Publication No. 8-41284 and Japanese Unexamined Patent Application Publication No. 8-239505, the shape, the grain diameter, and the addition amount of the brightening agent are restricted, and the appearance such as bright appearance and metallic appearance is limited by this restriction. Therefore, it is difficult to obtain a color tone having good metallic appearance as a substitute for painting and plating having a good appearance. Furthermore, the generation of the weld line is not prevented completely, and the cost may increase depending on the blending condition of materials.